1. Field of the Invention
The present invention relates to an EL (electroluminescent) device sealing plate, and a multiple sealing plate-producing mother glass substrate for producing a plurality of the EL device sealing plates, and in particular to an EL device sealing plate that has been processed into a recessed shape so as to cover an EL layered body formed on a substrate, and a multiple sealing plate-producing mother glass substrate for producing a plurality of the EL device sealing plates.
2. Description of the Related Art
There are passive and active EL devices.
The passive EL device has a simple matrix structure. In this simple matrix structure, first electrodes are disposed on a substrate, an EL layered body containing a light-emitting layer and then back electrodes as second electrodes are built up in this order on an upper surface of the first electrodes, and then sealing is carried out to keep out moisture and oxygen using a sealing plate that has been processed into a recessed shape so as to cover the EL layered body. With such a passive EL device, by controlling the shapes of the first electrodes, the light-emitting layer and the back electrodes, the light-emitting layer can be made to emit light selectively in accordance with the shape of the light-emitting layer; for example, by making the first electrodes and the back electrodes be mutually orthogonal stripes, matrix display can be carried out.
Moreover, the active EL device has an active matrix structure. In this active matrix structure, as with the structure of a TFT liquid crystal device, a thin film transistor circuit or a diode is formed on a substrate for each pixel, an EL layered body containing a light-emitting layer is built up on upper surfaces of the thin film transistor circuits or diodes, and then sealing is carried out to keep out moisture and oxygen using a sealing plate that has been processed into a recessed shape so as to cover the EL layered body. With such an active EL device, high-speed changing display can be carried out due to the high-speed switching ability of the thin film transistor circuits or diodes formed pixel by pixel, and hence such an active EL device is suited to display of moving images; it is thus thought that in the future, EL display apparatuses will primarily use active EL devices.
Furthermore, there are EL devices in which a bottom emission structure is adopted, and EL devices in which a top emission structure is adopted.
With an EL device in which a bottom emission structure is adopted, transparent members are used from the light-emitting layer toward and as far as the substrate, whereby the light emitted from the light-emitting layer is made to exit from the substrate side. With an EL device in which a top emission structure is adopted, transparent members are used from the light-emitting layer toward and as far as the sealing plate, whereby the light emitted from the light-emitting layer is made to exit from the sealing plate side.
However, with an active EL device, the thin film transistor circuits or diodes are not transparent, and hence if a bottom emission structure is adopted, then there will be parts where the light emitted from the light-emitting layer is blocked by the non-transparent film transistor circuits or diodes; the aperture ratio will thus be low, and hence the brightness relative to the inputted electrical power will be low.
Moreover, with an EL device in which a top emission structure is adopted, to make the aperture ratio high, and hence make the brightness relative to the inputted electrical power high, the sealing plate is required to have high transparency.
A glass material having high transparency is thus preferably used for the sealing plate. However, it is difficult to process a plate-shaped glass material into a recessed shape to obtain the sealing plate, and moreover the transparency is prone to dropping during this processing.